Method of forming a damascene structure with integrated planar dielectric layers

ABSTRACT

Methods are provided for forming a circuit component on a workpiece substrate. The methods comprise the steps of depositing a dielectric material over the substrate; etching a pattern through the dielectric material to expose a portion of the substrate; depositing a barrier metal over the dielectric material and the exposed portion of the substrate; depositing a conductive metal over the barrier metal, the deposited conductive metal having a thickness sufficient to fill the etched pattern; planarizing the conductive metal to form a planar metal layer; and polishing the metal layer and the barrier metal in a single polishing step using an abrasive-free polish until the dielectric material surrounding the pattern is exposed.

CROSS-REFERENCES TO RELATED APPLICATIONS

This is a division of application Ser. No. 10/942,302, filed Sep. 15,2004 now U.S. Pat. No. 7,229,907.

TECHNICAL FIELD

The present invention generally relates to damascene structures that arepart of a workpiece such as a semiconductor wafer, and more particularlyrelates to methods for forming and polishing damascene structures in amanner that produces planar layers.

BACKGROUND

Chemical mechanical polishing (CMP) is one technique which has beenconventionally used for semiconductor wafer planarization. For example,see U.S. Pat. No. 5,099,614, issued in March in 1992 to Riarai et al.;U.S. Pat. No. 5,329,732 issued July 1994 to Karlsrud et al., and U.S.Pat. No. 5,498,199 issued March 1966 to Karlsrud et al. A typical CMPapparatus suitable for planarizing a semiconductor surface generallyincludes a wafer carrier configured to support, guide, and applypressure to a wafer during the polishing process, a polishing compoundsuch as a slurry to assist in wafer surface material removal, and apolishing surface such as a polishing pad. In addition, the polishingapparatus may include an integrated wafer cleaning system and/or anautomated load/unload station to facilitate automatic processing of thewafers.

A wafer surface is generally polished by moving the wafer to be polishedrelative to the polishing surface in the presence of a polishingcompound. In particular, the wafer is placed in a carrier such that thesurface to be polished is placed in contact with the polishing surface,and the polishing surface and the wafer are moved relative to each otherwhile slurry is supplied to the polishing surface.

Furthermore, CMP is often applied when forming microelectronic devicesto provide a substantially smooth, planar surface suitable forsubsequent fabrication processes such as photoresist coating and patterndefinition. For example, a conductive feature such as a metal line,conductive plug, or the like may be formed on a wafer surface by formingtrench lines and vias on the wafer surface, depositing conductivematerial over the wafer surface and into the trenches and vias, andremoving the conductive material on the wafer surface using a CMPprocess, leaving the vias and trenches filled with conductive material.The conductive features often include a barrier material to reduceunwanted conductive material diffusion and to promote adhesion betweenthe conductive material and any adjacent layer in the circuit.

Aluminum is often used to form conductive features because itscharacteristics are compatible with conventional deposition (e.g.chemical vapor deposition) and etch (e.g., reactive ion etch)techniques. Although using aluminum to form conductive features isadequate in some cases, forming aluminum conductive features becomesincreasingly problematic as the size of the conductive featuredecreases. In particular, as the conductive feature decreases in size,the current density through the feature generally increases, and thusthe feature becomes increasingly susceptible to electromigration, i.e.,the mass transport of metal due to the current flow. Electromigrationmay cause short circuits where the metal accumulates, open circuitswhere the metal has been depleted, and/or other circuit failures.Similarly, increased conductive feature resistance may cause unwanteddevice problems such as access power consumption and heat generation.

Recently, techniques utilizing copper to form conductive features havebeen developed because copper is less susceptible to electromigrationand exhibits a lower resistivity than aluminum. Since copper does notreadily form volatile or soluble compounds, the copper conductivefeatures are often formed using a damascene process. More particularly,the copper conductive features are formed by creating a via within aninsulating material, depositing a barrier layer onto the insulatingmaterial surface and into the via, depositing a seed layer of copperinto the barrier layer, electrodepositing a copper layer onto the seedlayer to fill the via, and removing any excess barrier metal and copperfrom the insulating material surface using chemical and mechanicalpolishing. During the electrodeposition process, additives such asleveling agents may be added to the plating bath to reduce the formationof voids within the conductive features.

As stated previously, a CMP machine typically includes a wafer carrierconfigured to hold, rotate, and transport a wafer during the process ofpolishing or planarizing the wafer. During the planarizing operation, apressure applying element (e.g., a rigid plate, a bladder assembly, orthe like) that may be an integral part of the wafer carrier appliespressure such that the wafer engages a polishing surface with a desiredamount of force. The carrier and the polishing surface are rotated,typically at different rotational velocities, to cause relative lateralmotion between the polishing surface and the wafer and to promoteuniformed planarization. The polishing surface generally comprises ahorizontal polishing pad that may be formed of various materials such asblown polyurethane and are available commercially from, for example,Rodel Inc. located in Phoenix, Ariz. Abrasive slurry may also be appliedto the polishing surface which acts to chemically weaken the molecularbonds at the wafer surface so that the mechanical action of thepolishing pad and slurry abrasive can remove the undesirable materialfrom the wafer surface.

Unfortunately, the CMP process tends to leave stresses in the workpieceleading to subsequent cracking and shorting between metal layers.Furthermore, the CMP process may result in sheering or crushing offragile layers. The CMP process also has a tendency to cause dishing inthe center of wide metal features, such as trenches and vias, oxideerosion between metal features, and dielectric oxide loss.

For example, a conventional manufacturing process for a dual damascenestructure includes a step of polishing a low dielectric constantmaterial (i.e., k<2.6) to create a planar surface in preparation of acopper layer deposition. Planarizing the low dielectric constantmaterial is necessary because the low dielectric constant material isdeposited atop an underlying metal surface that generally hasundulations resulting from a prior CMP polishing step, and the lowdielectric constant material conforms to the underlying surfacetopography.

After the low dielectric constant material is polished, a copper layeris deposited into a via extending therethrough, and copper alsonaturally forms as a layer atop the low dielectric constant material.Using a CMP process, the copper layer is removed, leaving the lowdielectric constant material and an exposed copper surface inside thevia. The exposed copper typically has a dished surface following the CMPprocess. Consequently, the low dielectric constant material typicallymust be subjected to additional polishing after the copper CMP process.Polishing the low dielectric constant material is problematic. Thedielectric material is typically both porous and fragile, and as aresult is vulnerable to losing dielectric properties if water, watervapor, or other relatively high dielectric constant materials areentrained or adsorbed to the porous dielectric surface. Since manypolishing slurries are aqueous or have a relatively high dielectricconstant, it is difficult to polish without deteriorating the lowdielectric constant material's dielectric properties. One way to avoiddamaging the low dielectric constant material is to deposit a cappinglayer above the low dielectric constant material. The capping layerenables the dielectric stack to withstand friction at sustainedtemperatures as high as 400° C. A thin silicon carbide (SiC) materialcontaining hydrogen is particularly effective as the capping layer. SiChas a dielectric constant between 4.5 and 7.5. Another way to avoidoverstressing the material is to polish the exposed copper surfacewithin the via at very low pad pressures and moderate sheer rates.However, both of these preventive measures increase polish time anddecrease tool throughput.

One alternative to CMP for minimizing surface topography for a lowdielectric constant layer is the use of an abrasive-free polish (AFP)slurry to polish the underlying copper layer surface before depositing adielectric material thereon. Polishing copper using an AFP slurry is aparticularly effective way to minimize dishing, and consequentlyminimizes or eliminates corrective dielectric polishing following thecopper polishing. An AFP slurry effectively planarizes the coppersurface when the topography is already relatively flat and if there isnot a large copper overburden or field area thickness. However, not allcopper deposition processes result in a suitably flat copper surface ora sufficiently thin copper layer for the AFP slurry to be effective orefficient.

Electrochemical planarization, also known as electropolishing, isanother attractive alternative to CMP because it does not impartsignificant mechanical stresses to the workpiece, and consequently doesnot significantly reduce the integrity of the devices. Furthermore,electrochemical planarization is less likely to cause metal dishing,oxide erosion, and oxide loss of the dielectric layer.

Electrochemical planarization is based on electroetching andelectrochemical machining, that is, the removal of a thin layer of metalfrom a substrate through the action of an electrical solution andelectricity. For example, if two electrodes, an anode and a cathode areimmersed in a liquid electrolyte and are wired to permit a potentialdifference between the electrodes, metal atoms in the anode are ionizedby the electricity and go into the solution as ions. Depending on thechemistry of the metals and salt, the metal ions from the anode tend toeither plate the cathodes, fall out as precipitate, or remain insolution. Unfortunately, using conventional electrochemicalplanarization techniques, etching selectivity is reduced in areas on thewafer having varying high or low topographies, and uniform planarizationis not achieved. The same is largely true when a polish pad is used inconjunction with an electrochemical planarization process, in which casethe process is referred to as electrochemical mechanical planarization,or ECMP.

Accordingly, it is desirable to overcome some of the difficultiesassociated with forming a damascene structure, particularly one thatincludes an interlayer dielectric structure with multiple dielectriclayers. Particularly, it is desirable to overcome problems related tosurface topography on a metallization or dielectric layer due to unevenlayer deposition, and to overcome associated difficulties in planarizinglow dielectric constant materials formed around or above themetallization layer. Furthermore, other desirable features andcharacteristics of the present invention will become apparent from thesubsequent detailed description and the appended claims, taken inconjunction with the accompanying drawings and the foregoing technicalfield and background.

BRIEF SUMMARY

According to one embodiment of the invention, a method is provided forforming a circuit component on a workpiece substrate. The methodcomprises the steps of depositing a dielectric material over thesubstrate; etching a pattern through the dielectric material to expose aportion of the substrate; depositing a barrier metal over the dielectricmaterial and the exposed portion of the substrate; depositing aconductive metal over the barrier metal, the deposited conductive metalhaving a thickness sufficient to fill the etched pattern; planarizingthe conductive metal to form a planar metal layer; and polishing themetal layer and the barrier metal in a single polishing step using anabrasive-free polish until the dielectric material surrounding thepattern is exposed.

According to another embodiment of the invention, a method is providedfor forming a multiple-layer structure on a workpiece with a circuitcomponent extending through the structure. The method comprises a stepof forming a first layer of the circuit component by a) depositing adielectric material onto the workpiece; b) etching a pattern through thedielectric material to expose a surface beneath the dielectric material;c) depositing a barrier metal over the dielectric material and theexposed surface; d) depositing a conductive metal over the barriermetal, the deposited conductive metal having a thickness sufficient tofill the etched pattern; e) planarizing the conductive metal to form aplanar metal layer; and f) polishing the metal layer and the barriermetal in a single polishing step using an abrasive-free polish until thedielectric material surrounding the filled pattern is exposed. Themethod further comprises the step of forming a plurality of additionallayers over the first layer by repeating steps a) through f) to producethe multiple-layer structure with the circuit component formed ofconnected filled patterns from each of the multiple layers.

According to another embodiment of the invention, another method isprovided for forming a multiple-layer structure on a workpiece with acircuit component extending through the structure. The method comprisesthe steps of depositing a first dielectric material having a dielectricconstant greater than about 2.6 onto the workpiece; planarizing thefirst dielectric material; depositing a second dielectric materialhaving a dielectric constant less than about 2.6 over the firstdielectric material; etching a pattern through the first and seconddielectric materials to expose a surface beneath the first dielectricmaterial; depositing a barrier metal over exposed areas of the first andsecond dielectric material and over the exposed surface; depositing aconductive metal over the barrier metal, the deposited conductive metalhaving a thickness sufficient to fill the etched pattern; planarizingthe conductive metal to form a planar metal layer; and polishing themetal layer and the barrier metal in a single polishing step using anabrasive-free polish until the second dielectric material surroundingthe filled pattern is exposed, and stopping the polishing step beforethe second dielectric material is polished.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereinafter be described in conjunction withthe following drawing figures, wherein like numerals denote likeelements, and

FIG. 1 is a cross-sectional view of an interconnection formed using anexemplary process according to the present invention;

FIGS. 2 to 4 are cross-sectional views illustrating a process forforming the interconnection depicted in FIG. 1;

FIG. 5 is a top cutaway view of a polishing system in accordance withthe present invention; and

FIG. 6 is a cross-sectional view of a portion of an electrochemicaldeposition and polishing apparatus in accordance with an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Furthermore, there is no intention to be bound by anyexpressed or implied theory presented in the preceding technical field,background, brief summary or the following detailed description.

The present invention overcomes some of the difficulties associated withforming an interlayer dielectric structure with multiple planardielectric layers. For example, the invention overcomes problems relatedto surface topography on a metallization or dielectric layer due touneven layer deposition, and also overcomes difficulties in planarizinglow dielectric constant materials. The solution to these difficultieslies in an inventive integrated process that combines metallizationlayer planarization and polishing to produce a structure having metalembedded in a low dielectric constant material with a barrier metal onthe structure's exposed working surface. The process can be supplementedwith a simplified barrier removal process that does not necessarilyrequire depositing a conventional capping layer onto the low dielectricconstant material, and further avoids potential damage to the lowdielectric constant material that can be caused by overpolishing themetallization or barrier layers. The process can be further supplementedby a step that includes adding a hard dielectric layer to the structureas necessary to provide an easily polished surface and thereby avoid anypolishing on the low dielectric constant material.

An exemplary damascene structure prepared by the process of the presentinvention is illustrated in FIG. 1 which is a cross-sectional view of aninterconnection formed using an exemplary process according to thepresent invention. The interconnection structure is formed on asubstrate 32 having a region 30 on which the interconnection is to beformed, and includes multiple metallization layers 40 a-d with barriermetal 38 a-d at least partially surrounding the metallization layers 40a-d. The metallization layers 40 a-d are formed through respectivedielectric layers 34, 36 a-c. Although the interconnection structure isillustrated as four-layered, it is understood that the number of layersis not a limiting feature of the invention, and the process of thepresent invention can be utilized to produce an interconnectionstructure or other circuit pattern having fewer or many moremetallization layers than four. The interconnection structure or othercircuit pattern, and the method of manufacturing the same will bedescribed in detail below.

FIG. 2 illustrates a single dielectric layer 34 that is deposited ontothe substrate 32 over the region 30. The various materials andproperties for the dielectric layer 34 will be described in detailbelow. The dielectric layer 34 can be deposited using a plasma enhancedchemical vapor deposition process, a spin coating process, or otherconventional process suitable for forming a layer from a particulardielectric material. A via or trench line 35 is etched through thedielectric layer 34 to expose the circuit component 30, and the barriermetal 38 a is deposited over the exposed surfaces including thesubstrate 32, the circuit component 30, and the dielectric layer 34.Exemplary barrier metals include titanium (Ti), titanium nitride (TiN),tantalum (Ta), tantalum nitride (TaN), and other conventional barriermetal compounds. The barrier metal 38 a is approximately 50 Å inthickness, although the barrier metal 38 a can be thinner or thicker asnecessary.

FIG. 3( a) illustrates a metallization layer 40 a conformally depositedover the barrier metal 38 a, and FIG. 3( b) illustrates themetallization layer 40 a deposited over the barrier metal 38 a using aplanar plating process described in detail below. Either process fordepositing the metallization layer 40 a is within the scope of thepresent invention, and is preliminary to the structure of FIG. 4 whichillustrates the completed interconnection layer after polishing themetallization layer 40 a and the barrier metal 38 a.

In an exemplary embodiment, each of the metallization layers 40 a-d iscopper. Each of the metallization layers 40 a-d is preferably depositedand polished using an apparatus that is suitable for chemically,mechanically, and/or electrochemically depositing conductive materialonto a workpiece surface, and also is suitable for planarizing theconductive material. FIG. 5 illustrates a top cutaway view of one suchsuitable polishing apparatus 100 in accordance with the presentinvention. The apparatus 100 includes a multi-station polishing system102, a clean system 104, and a wafer load/unload station 106. Inaddition, the apparatus 100 includes a cover (not shown) that surroundsthe apparatus 100 to isolate the apparatus 100 from the surroundingenvironment. In accordance with a preferred embodiment in the presentinvention, the apparatus 100 is a CMP machine available from NovellusSystems Inc. of San Jose, Calif. However, the apparatus 100 may be anymachine capable of removing or depositing material from or onto aworkpiece surface.

Although the apparatus 100 and other machines described below may beused to remove material or deposit material on the surface of a varietyof workpieces such as magnetic disks, optical disks, and the like, themachines are conveniently described below in connection with removingand depositing material on the surface of a wafer. In the context of thepresent invention, the term “wafer” shall mean semiconductor substrates,which may include layers of insulating, semiconductor, and conductinglayers or features formed thereon and used to manufacturemicroelectronic devices.

An exemplary polishing station 102 includes four independently operatingpolishing stations 108, 110, 112, and 114; a buff station 116; a stage118; a robot 120; and optionally, a metrology station 122. The polishingstations 108-114 may be configured as desired to perform specificfunctions. In accordance with the present invention, at least one of thestations 108-114 includes an electrochemical deposition and polishingapparatus as described herein. Another one of the stations 108-114includes an electrochemical planarization apparatus as described herein,and the remaining stations may be configured for traditional chemicalmechanical polishing or the like.

The polishing system 102 also includes polishing surface conditioners140 and 142. The surface conditioner configuration generally depends onthe type of polishing surface to be conditioned. For example, when thepolishing surface comprises a polyurethane polishing pad, theconditioners 140 and 142 may include a rigid substrate coated withdiamond material. Various other surface conditioners may also be used inaccordance with the present invention.

The clean system 104 is generally configured to remove debris such asslurry residue and material from the wafer surface during polishing. Inaccordance with the illustrated embodiment, the clean system 104includes clean stations 124, 126, a spin rinse dryer 128, and a robot130 configured to transport the wafer between the clean stations 124,126 and spin rinse dryer 128. Alternatively, the clean station 104 maybe separate from the remainder of the electrochemical deposition andplanarization apparatus. In this case, the load station 106 isconfigured to receive dry wafers for processing, but the wafers mayremain in a wet (e.g., deionized water) environment until the wafers aretransferred to the clean station. In operation, cassettes 132, includingone or more wafers, are loaded onto the apparatus 100 at the station106. The wafers are then individually transported to a stage 134 using adry robot 136. A wet robot 138 retrieves a wafer at the stage 132 andtransports the wafer to the metrology station 122 for filmcharacterization or to the stage 118 within the polishing system 102.The robot 120 picks up the wafer from the metrology station 122 or thestage 118 and transports the wafer to one of the polishing stations108-114 for electrochemical deposition or planarization of a conductivematerial. After a desired amount of material has been deposited orremoved, the wafer may be transported to another polishing station.Alternatively, as will be more fully discussed below, a polishingenvironment within one of the stations may be changed from anenvironment suitable for the electrochemical deposition to anenvironment suitable for electrochemical planarization; e.g., bychanging the solution and the bias applied to the wafer. In this case, asingle polishing station may be used to both deposit material and removematerial from the wafer.

After conductive material has been either deposited or removed from thewafer surface, the wafer is transferred to the buff station 116 tofurther polish the surface of the wafer. After the polishing and/or buffprocess, the wafer is transferred to the stage 118 which is configuredto maintain one or more wafers in a wet (e.g. deionized water)environment.

After the wafer is placed in the stage 118, the robot 138 picks up thewafer and transports it to the clean system 104. In particular, therobot 138 transports the wafer to the robot 130, which in turn placesthe wafer in one of the clean stations 124, 126. The wafer is cleanedusing one or more of the stations 124 and 126 and then is transported tothe spin rinse dryer 128 to rinse and dry the wafer prior totransporting it to the load/unload station 106 using the robot 136.

Returning to FIG. 3, an exemplary embodiment of the invention involves amethod that includes the steps of depositing the copper layers 40 a-donto the barrier metal 38 a-d, and planarizing the copper using acombined planar plating process and an abrasive-free polishing processto produce a structure containing barrier metal 38 a-d on the dielectricmaterial field, and very planar copper in the features such as thetrench line or via 35 and also overlying the dielectric material 34.Following a below-described simplified barrier removal step that doesnot require a conventional capping layer or any polishing of thedielectric material 34, a very planar overall layer is preparedincluding the dielectric material 34 and the embedded copper layer 40 aas illustrated in FIG. 4. Planar plating is a technique that includeselectroplating copper onto a seed layer to fill features such as thetrench line or via 35 in a bottom-up manner. Planar plating provides athin and very planar exposed overburden of copper in the range of lessthan about 3000 Å. The planar plating process involves creating featurefilling contrast by rubbing a wafer surface with a polishing pad beforeand/or during plating.

In accordance with one embodiment of the invention, an apparatus 150shown in FIG. 6 is configured to perform electrochemical deposition,electrochemical planarization, and/or polishing, utilizing aplaten/polishing pad stack 180 that can also be utilized or easilymodified for use with conventional apparatuses such as the abovedescribed apparatus 100 and the various associated components. Theapparatus 150 includes the stack 180, a wafer 200 carried by a carrierassembly (not shown), a source of potential 300, a source of temperaturecontrolled electrolytic solution 240, and drive controller 250. Ingeneral, the apparatus 150 is configured to electrochemically depositonto or remove material from a surface of the wafer 200. The apparatus150 is further configured to polish the wafer 200.

A conductive material 220 is disposed within the stack 180 which alsoincludes a platen 210 and a polishing pad 230. During a depositionprocess, the conductive material 220 is coupled to the anode of a sourceof the supply voltage 300, and a second conductive material (not shown)is coupled to the wafer 200. By reversing the polarity, the processbecomes an electro-polishing process.

There are several ways to introduce an electrolyte solution 260 to theinterface between the polishing pad 230 and the wafer 200. Threeexemplary methods are illustrated in FIG. 6, although only one methodwould typically be utilized for a given apparatus, and the three methodsare illustrated merely for illustration. In one exemplary embodiment,the platen 210, conductive material 220, and polishing pad 230 haveopenings 270, 280, 290 therethrough to enable delivery of electrolytesolution 260 from the reservoir 240 through the polishing pad to reachthe interface between the polishing pad 230 and the wafer 200. Inanother exemplary embodiment, the openings 270 and 280 lead theelectrolyte solution 260 to the polishing pad that is formed from aporous material that absorbs the electrolyte solution 260 and allows theelectrolyte 260 to seep out to the interface between the polishing pad230 and the wafer 200. In yet another embodiment, the electrolyte 260 ispoured onto the polishing pad 230 through a faucet 265.

As stated previously, electrochemical deposition results when therequired potential difference is applied between the wafer 200 and theconductive material 220. Since the electrolyte solution is beingprovided to the region between the polishing pad 230 and the wafer 200,copper is electrochemically deposited on the wafer 200. Of course, itshould be understood that a thin seed layer of copper must first bedeposited on the wafer 200. This may be accomplished by forming a seedlayer of copper on the surface of the wafer 200 as, for example, bysputtering, chemical vapor deposition, or any other suitable depositionmethods. In particular, the power supply 300 applies a relative positivecharge to conductive material 220 and a relative negative charge to thewafer 200.

The platen assembly having the polishing pad 230 disposed thereon isgenerally configured to move relative to the wafer 200 to facilitatewafer polishing and to promote a uniform deposition of material onto thewafer 200. The platen assembly may be connected to a drive motorassembly 250 that is operative to rotate the platen and polishingsurface about a vertical axis. It will be appreciated, however, that thedrive or motor assembly may be operative to move the platen assembly andpolishing surface in an orbital, linear, rotational, or oscillatorypattern or any combination thereof. For example, U.S. Pat. No. 5,582,534(Sheldon et al.) and U.S. Pat. No. 5,938,884 (Hoshizaki et al.) discloseseveral mechanisms for creating an orbital motion.

The electrolytic solution contained in the reservoir 240 includes thesuitable precursors to the material being deposited onto the wafersurface. If the metallization layers include or consist of copper, avariety of copper salts may be employed in the electrolytic solution asa source of copper ions including, for example, copper sulfates, copperacetates, copper fluoroborate, and cupric nitrates. The copper salts maybe suitably present in a relatively wide concentration range.Preferably, a copper salt will be employed at a concentration of fromabout 10 to about 300 grams/liter of composition.

The electrolyte solution typically includes suppressants, andaccelerators as necessary. In an exemplary embodiment, the accelerant isincluded in the electrolyte solution with the copper salts. In anotherexemplary embodiment, the barrier metal surface is first activated withan accelerant and the accelerant is selectively removed from some of theexposed surface area to yield a plating rate contrast. The acceleratormay be formulated for preferential adsorption within the features of thework piece, particularly within the narrow, high aspect ratio features.The accelerator may also be formulated so that it lowers the energybarrier required to cause deposition of the copper on the wafer surface.The accelerator may serve as a complexing agent that forms stablecomplexes with the copper. While copper may deposit on the work piece ata standard reduction potential, the copper may form a complex with theaccelerator and have a reduction potential less than the standardreduction potential. Thus, less electricity would be required during theelectrodeposition process to break the bonds of the accelerator/coppercomplex and deposit the copper onto the work piece. Alternatively, anaccelerator may be selected so that an accelerator/copper complex isformed requiring a particular reduction potential. Depending on thevalue of this reduction potential, the amount and length of currentsupplied to the electrodeposition process can be varied so that thecopper is deposited in varying grain size. In one exemplary embodimentof the invention, the accelerators include compounds that contain one ormore sulfur atoms and have a molecular weight of about 1000 or less. Forsuch an embodiment, the accelerators preferably include compounds havingan —S—S— moiety, or compounds having the formula H—S—R, wherein R is anelectron-donating group that increases electron density on the sulfuratom and impart stability to the accelerator anion that is created insolution. Co-pending U.S. application Ser. No. 10/666,432, filed Sep.18, 2003 and entitled “Methods for Depositing Copper on a Noble MetalLayer of a Work Piece” is incorporated herein by reference and disclosesspecific accelerators as well as suppressants and other agents that maybe utilized in the planar plating process in accordance with the presentinvention.

The planar plating process is performed until the structure appears asdepicted in FIG. 3, with the copper layer 40 a filling the trench lineor via 35 over the barrier metal 38 a and also overlying the barriermetal 38 a in areas that are directly over the dielectric material 34.The copper layer 40 a overlying the barrier metal 38 a is effectivelyplanarized to be between about 500 Å and about 3000 Å. At this point,the planar plating process ends and both the copper layer 38 a and thebarrier metal are together removed using a CMP process that includes theuse of an AFP solution until the structure appears as depicted in FIG.4. The AFP step is stopped when the planar dielectric material 34surrounding the trench line or via 35 is exposed but before the planardielectric material 34 is subjected to any polishing.

The abrasive-free polishing solution is an aqueous solution, and ispreferably a basic solution such as a KOH solution. The solutionoxidizes the copper metallization layer 40 a and the barrier metal 38 ato provide a corroded metal surface that is easily removed using apolishing pad. The absence of abrasive particles in the solution allowsthe metallization layer 40 a and the barrier metal 38 a to be removedwithout being scratched or unevenly polished due to abrasive build up.

After the process described above with reference to FIGS. 2 to 4 iscompleted, a planar surface is provided on which additional dielectricmaterial 36 a is deposited, etched to form a trench line or via that isabove and continuous with via 35, and filled with a barrier metal 38 band a metallization layer 40 b. The process is then repeated to formadditional layers as illustrated in FIG. 1, without ever planarizing thedielectric material.

The process described above with reference to FIGS. 2 to 4 is bothunique and particularly beneficial when the damascene structure includesa low dielectric material forming some or all of the dielectric layers34, 36 a-c. Dielectric materials having a dielectric constant less thanabout 2.6 are fragile and porous, and consequently do not withstand themechanical and chemical stresses associated with polishing. The processof the present invention overcomes difficulties associated with lowdielectric constant materials as the process enables production ofstacked planar layers without any dielectric layer polishing.Discontinuous line 39 in FIG. 4 illustrates a depth for whichoverpolishing is performed in prior processes in order to correct formetal dishing. Some interconnect patterns or trench lines must be verydeep, requiring a damascene process to be repeated for up to ten or morelayers using conventional processes. Because the low dielectric constantmaterial 34 is not polished according to the processes of the presentinvention, the number of layers for interconnect patterns or trenchlines is substantially reduced. Another consequential benefit is adecrease in the total amount of metal wasted in overpolishing associatedwith each metallization line and better control of feature geometries.

Although the process described above enables stacked low dielectricconstant layers to be formed without ever planarizing the low dielectricconstant material, minor topographical imperfections may exist after aplurality of layers are formed. Typically some imperfections appearevery two to four layers of low dielectric constant material. In orderto avoid perpetuating the topographical perfections through the entireinter-layer dielectric stack, an exemplary embodiment of the inventionincludes the step of depositing a “planarization layer” as one layersuch as layer 34 in FIGS. 1 to 4. The planarization layer is depositedevery two to four layers of the inter-layer dielectric stack. Theplanarization layer is formed from a high mechanical strength dielectricmaterial, and replaces one of the low dielectric constant materiallayers. Exemplary high mechanical strength dielectric layers have adielectric constant higher than about 2.6 and include non-poroustetraethoxysilane (TEOS) films and SiC or SiOC films made from materialsunder the product names SiC or CORAL of Novellus Systems, Inc. Theplanarization layer is deposited using a conventional process and can beplanarized using a CMP process. Because the planarization layer is onlydeposited every 2 to 4 layers, the overall inter-layer dielectricstructure is predominantly formed from a low dielectric constantmaterial and performs with improved low resistance in comparison withconventional inter-layer dielectric structures.

To minimize performance losses associated with the hard dielectricmaterial, the planarization layer is formed in two steps according toone exemplary embodiment of the invention. First, only a portion of theplanarization layer is deposited using a plasma enhanced chemical vapordeposition process, a spin coating process, or other conventionalprocess suitable for forming a layer from a particular dielectricmaterial, and the planarization layer is planarized using a CMP process.The planarization layer is preferably planarized to a thicknesssubstantially equal to the height of the via that is to be etched later,although the layer can effectively be formed thinner or thicker than thevia height. A layer of low dielectric constant material is thendeposited on top of the hard layer up to the full height of the trenchlines that are to be etched. The planarization layer and the lowdielectric constant material are then simultaneously patterned andetched as a one-step dual damascene process without planarizing the lowdielectric constant material. In an alternate embodiment, the process isperformed in two sequential single damascene process steps. Eitherprocess enables the planarization layer to have a minimal thickness.

The above-described process overcomes some of the difficultiesassociated with forming an interlayer dielectric structure with multiplelayers, including problems related to surface topography on ametallization or dielectric layer, and non-planar low dielectricconstant materials. The process further overcomes problems associatedwith removing barrier metal that is disposed over a low dielectricconstant material without requiring a conventional capping layer on thelow dielectric constant material.

While at least one exemplary embodiment has been presented in theforegoing detailed description, it should be appreciated that a vastnumber of variations exist. It should also be appreciated that theexemplary embodiment or exemplary embodiments are only examples, and arenot intended to limit the scope, applicability, or configuration of theinvention in any way. Rather, the foregoing detailed description willprovide those skilled in the art with a convenient road map forimplementing the exemplary embodiment or exemplary embodiments. Itshould be understood that various changes can be made in the functionand arrangement of elements without departing from the scope of theinvention as set forth in the appended claims and the legal equivalentsthereof.

1. A method of forming a damascene structure on a substrate, the methodcomprising the steps of: depositing a dielectric material over thesubstrate; etching a pattern through the dielectric material to expose aportion of the substrate; depositing a barrier metal over the dielectricmaterial and the exposed portion of the substrate; depositing aconductive metal over the barrier metal, the deposited conductive metalhaving a thickness sufficient to fill the etched pattern; planarizingthe conductive metal to form a planar metal layer over the barrierlayer; and polishing the metal layer and the barrier metal in a singlepolishing step until the dielectric material surrounding the pattern isexposed.
 2. The method according to claim 1, wherein the step ofpolishing the metal layer and the barrier layer is stopped before thedielectric material is polished.
 3. The method according to claim 1,wherein the conductive metal is copper.
 4. The method according to claim1, wherein the dielectric material has a dielectric constant of lessthan about 2.6 .
 5. The method according to claim 1, wherein the stepsof depositing and planarizing the conductive metal are performedsimultaneously using a process comprising the steps of: electroplatingthe conductive metal onto an exposed workpiece surface by application ofa predetermined current density to the workpiece; and rubbing theexposed workpiece surface with a polishing pad during at least theelectroplating step.
 6. The method according to claim 5, wherein theelectroplating step comprises applying the predetermined current densitywhile exposing the exposed workpiece to an electrodeposition compositioncomprising a metal salt, a suppressor, and an electrolyte.
 7. The methodaccording to claim 6, wherein the electrodeposition composition furthercomprises an accelerator.
 8. The method according to claim 6, furthercomprising the step of exposing selected portions of the exposedworkpiece to an accelerator before the electroplating step.
 9. Themethod according to claim 1, wherein the planarization step comprisesplanarizing the conductive metal layer until the planar metal has athickness ranging up to about 3000 Å.
 10. The method according to claim1, wherein the polishing step is performed using an abrasive-freepolish.